Effect of positive pressure on venous return in volume-loaded cardiac surgical patients

• Published in: Journal of applied physiology (1985) Vol. 92; no. 3; pp. 1223 - 1231
• Main Authors: Van Den Berg, Paul C. M, Jansen, Jos R. C, Pinsky, Michael R
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Am Physiological Soc 01.03.2002; American Physiological Society
• Subjects: Abdomen - physiopathology; Atrial Function, Right; Biological and medical sciences; Blood Volume; Cardiac Output; Coronary Artery Bypass; Fluid Therapy; Heart; Humans; Inhalation; Lungs; Medical sciences; Positive-Pressure Respiration; Postoperative Period; Pressure; Respiratory system; Respiratory System - physiopathology; Resuscitation; Surgery (general aspects). Transplantations, organ and tissue grafts. Graft diseases; Surgery of the heart; Veins - physiopathology; Heart; Human; Assisted ventilation; Positive pressure; Surgery; Interaction; Lung; Venous return; Cardiovascular disease; Mechanical ventilation; Monitoring; Venous pressure
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00487.2001

1  Department of Intensive Care, Leiden University Medical Centre, 2300 RC Leiden, The Netherlands; and 2  Department of Anesthesiology and Critical Care Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261 The hemodynamic effects of increases in airway pressure (Paw) are related in part to Paw-induced increases in right atrial pressure (Pra), the downstream pressure for venous return, thus decreasing the pressure gradient for venous return. However, numerous animal and clinical studies have shown that venous return is often sustained during ventilation with positive end-expiratory pressure (PEEP). Potentially, PEEP-induced diaphragmatic descent increases abdominal pressure (Pabd). We hypothesized that an increase in Paw induced by PEEP would minimally alter venous return because the associated increase in Pra would be partially offset by a concomitant increase in Pabd. Thus we studied the acute effects of graded increases of Paw on Pra, Pabd, and cardiac output by application of inspiratory-hold maneuvers in sedated and paralyzed humans. Forty-two patients were studied in the intensive care unit after coronary artery bypass surgery during hemodynamically stable, fluid-resuscitated conditions. Paw was progressively increased in steps of 2 to 4 cmH 2 O from 0 to 20 cmH 2 O in sequential 25-s inspiratory-hold maneuvers. Right ventricular (RV) cardiac output (CO td ) and RV ejection fraction (EF rv ) were measured at 5 s into the inspiratory-hold maneuver by the thermodilution technique. RV end-diastolic volume and stroke volume were calculated from EF rv and heart rate data, and Pra was measured from the pulmonary artery catheter. Pabd was estimated as bladder pressure. We found that, although increasing Paw progressively increased Pra, neither CO td nor RV end-diastolic volume changed. The ratio of change ( ) in Paw to Pra was 0.32 ± 0.20. The ratio of Pra to CO td was 0.05 ± 00.15 l · min 1 · mmHg 1 . However, Pabd increased such that the ratio of Pra to Pabd was 0.73 ± 0.36, meaning that most of the increase in Pra was reflected in increases in Pabd. We conclude that, in hemodynamically stable fluid-resuscitated postoperative surgical patients, inspiratory-hold maneuvers with increases in Paw of up to 20 cmH 2 O have minimal effects on cardiac output, primarily because of an in-phase-associated pressurization of the abdominal compartment associated with compression of the liver and squeezing of the lungs. abdominal pressure; heart-lung interaction; hemodynamic monitoring; human study; mechanical ventilation; preload